1. Field of the Invention
The present invention relates to a magnetic head assembly used in a magnetic disk apparatus for recording information on and reproducing information from a recording medium, and more particularly to an improved method of manufacturing a head.
2. Description of the Background Art
Digital magnetic recording devices for data storage generally comprise a thin film magnetic recording disk and a recording head which is moved above the surface of the rotating disk to read and write information on the disk. Advanced slider head assemblies generally comprise a rigid substrate for the slider, a recording head, and protective overcoat films.
During operation of the disk drive system, an actuator mechanism moves the magnetic transducer to a desired radial position on the surface of the rotating disk where the recording head reads or writes data. The slider is generally rectangular in shape and the recording head usually comprising a separate read and write element is formed on an end surface of the slider. Typically this end surface of the slider will constitute the slider trailing surface when the slider head assembly is suspended above a rotating disk.
The slider portion, which constitutes the bulk of the slider head assembly is made of a ceramic substrate such as alumina-titanium carbide or another suitable material. The recording head portion of the slider head assembly typically is a sequence of thin layers of insulating materials such as alumina along with the recording head comprising the read head and the write head. The read and write heads are generally comprised of a sequence of several thin metallic films.
The slider generally serves to mechanically support the head and any electrical connections between the recording head and the rest of the disk drive system. One surface of the slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk. This surface is the airbearing surface. The magnetically active ends of the recording head are positioned on the air bearing surface.
In high density magnetic recording, it is important to maintain clearance between the slider on which the recording head is attached and the rotating disk upon which data is recorded and subsequently recovered during read back. This clearance is required in order to achieve a mechanical interface which has high reliability. It is also desirable to minimize the spacing between the recording head and the rotating disk in order to achieve high recording density. In order to simultaneously achieve both of these requirements it is advantageous during the operation of a disk drive to have the lowest point of both the slider and the recording head be the same distance from the disk.
Final dimensional control of the slider head assembly is achieved by lapping. The electrically active recording head exposed at the air bearing surface are generally softer than the ceramic slider body. As a consequence, the particles used in the conventional lapping process of the slider tend to erode the softer materials faster than the harder slider body. This results in a recession of the recording head away from the air bearing surface of the slider increasing the total distance from the recording head to the recording disk. This recession is sometimes called pole tip recession because it is measured from the pole tips of the recording head. Typically recording heads are recessed from the alumina overcoat and usually the overcoat is recessed from the air bearing surface.
Pole tip recession is a common feature when conventional lapping processes are used. Conventional lapping processes utilize either oscillatory or rotary motion of the slider head assembly workpiece across either a rotating or oscillating lapping plate to provide a random motion of the workpiece over the lapping plate and randomize plate imperfections across the slider head surface in the course of lapping. The amount of recession is influenced by the slurry chemistry, the lapping speed and time, lapping pressure, the roughness of the pad or plate, and the temperature during the process. Ordinarily a layer of alumina, Al2O3, is formed on the trailing surface of the slider and recording head. The metallic structure of the recording head is formed on this insulating layer disposed on the slider and then an overcoat layer, usually alumina, is formed over the recording head. Generally the overcoat layer is much thicker than the insulating layer. While there have been attempts in the past to improve the recession by altering the lapping process, these attempts have generally been focussed on the recession as defined from the air bearing surface of the slider to the alumina overcoat.
Magnetically, the important spacing is from the pole tips to the recording media. Any recession of the pole tips from the air bearing surface of the slider is generally not useful. The total recession from the air bearing surface to the pole tips is the sum of a first recession from the air bearing surface to the overcoat and a second recession from the overcoat to the pole tips. It is possible to have protrusion or negative recession, but this is uncommon and usually both first and second recessions are typically recessed away from the recording disk.
The manufacturing processes carried out to achieve lapping result in a distribution of recession values. The two most important aspects of recession are the average value and the distribution of those values for a large number of slider head assemblies. Generally the distribution of the recession values from the air bearing surface to the alumina layers is more narrowly distributed compared to the recession values from the alumina layers to the recording head. Thus, the biggest contributor to the width of the distribution of the total recession distribution is the width of the distribution of the distances from alumina to pole tips. Accordingly there is a need for a process which allows for reduced alumina to pole tip recession and more precision in controlling the alumina to pole tip recession.
To achieve the above and other objects, there is provided a method of controlling the relative recession distances between the alumina layers and the metallic recording head structure during the lapping process of a slider head assembly. This method takes advantage of the fact that the insulating and overcoat layers, not limited to but most commonly alumina, have a different thermal expansion coefficient than the metallic head structure. By placing the combined structure in a controlled thermal environment during the lapping procedure, the relative offset between the head and the insulating and overcoat layers can be controlled with more precision. This results in a recession distribution in which the mean is better controlled and the distribution is substantially improved.
The preferred embodiment is to pass a current through the write head portion of the recording head during the lapping process of a slider head assembly. This has several advantages including being relative easy to implement. The heat from the current dissipation in the write head coil is delivered precisely to the head structure and the surrounding layers. It is desired that the coefficient of thermal expansion for the insulating and overcoat layers be greater than for the metallic head structure. There are many useful combinations of alloys and overcoat layers that meet this criterion.
An alternative embodiment of this invention is to cool the head and overcoat relative to ambient temperatures. This is the preferred method when the coefficient of thermal expansion for the insulating and overcoat layers is less than that of the metallic head structure.
Most lapping processes in current use are designed for rows of sliders. A row of sliders is a sequence of recording head structures on a common ceramic substrate before the substrate is separated into individual sliders. A row may contain 40 to 50 slider head assemblies before final separation into individual sliders. More precision is possible when lapping each individual slider after separation from rows. One advantage of the present invention is that it is easily implemented for either row lapping or individual slider lapping.